bpf, sockmap: Do not inc copied_seq when PEEK flag set

When data is peek'd off the receive queue we shouldn't considered it
copied from tcp_sock side. When we increment copied_seq this will confuse
tcp_data_ready() because copied_seq can be arbitrarily increased. From
application side it results in poll() operations not waking up when
expected.

Notice tcp stack without BPF recvmsg programs also does not increment
copied_seq.

We broke this when we moved copied_seq into recvmsg to only update when
actual copy was happening. But, it wasn't working correctly either before
because the tcp_data_ready() tried to use the copied_seq value to see
if data was read by user yet. See fixes tags.

Fixes: e5c6de5fa0258 ("bpf, sockmap: Incorrectly handling copied_seq")
Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20230926035300.135096-3-john.fastabend@gmail.com

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index 81f0dff69e0b69bcc03bd932dcc42a8578939ecb..32726820300156322168e7696e38adae322ab43a 100644 (file)
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -222,6 +222,7 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk,
                                  int *addr_len)
 {
        struct tcp_sock *tcp = tcp_sk(sk);
+       int peek = flags & MSG_PEEK;
        u32 seq = tcp->copied_seq;
        struct sk_psock *psock;
        int copied = 0;
@@ -311,7 +312,8 @@ msg_bytes_ready:
                copied = -EAGAIN;
        }
 out:
-       WRITE_ONCE(tcp->copied_seq, seq);
+       if (!peek)
+               WRITE_ONCE(tcp->copied_seq, seq);
        tcp_rcv_space_adjust(sk);
        if (copied > 0)
                __tcp_cleanup_rbuf(sk, copied);